THE EFFECT OF SOIL ELECTRICAL PARAMETERS ON RADIOW AVE PROPAGATION IN SELECTED LOCATIONS IN NIGERIA

Abstract

Thisreport presents the results of the estimation of soil dielectric permittivity of different types of soil across Nigeria. Other parameters measured are: soil volumetric moisture content, soil temperature, humidity and pressure. The study covers an area of about 9 x 105km2. The capacitance probe method and the telemetry method using wireless Vantage Pro 2 transmitter and receiver were employed to measure the soil parameters. The soil types encountered in the course of the work are sandy clay loam, heavy clay, clay, sandy clay, clay loam, sandy loam and loamy sand. Using the capacitance probe method, the soils were probed with aluminum plates, steelplates and iron rods to a depth of 60 em with varied probe spacing of between 50 em to 250 cm/300 em, Two major components of permittivity were measured; complex and relative permittivity. The -results obtained using aluminum plates showed that complex permittivity values ranged from 5.268 x 10-9 Fm-I in Kaduna (Heavy clay) to 9.8 x 10-13 Fm-1 in Ilorin (sandy clay loam).This was closely followed by the results obtained using steel plates which ranged from 3.979 x 10-9 Fm-I, Kana (sandy clay loam) to 9.080 x 10-13 Fm-I, Off a (sandy clay loam). For the iron rods, the permittivity values ranged from 3.274 x 10-9 Fm-I (Kaduna) to 1.856 x 10-11 Fm-I in Okitipupa (sandy clay). The results generally revealed that permittivity is not only dependent on the soil types but also on the material of the probe used (plate or rod), probe depth, probe spacing or spread and as well as cationic species present in the soil. On the other hand using the telemetry method, the relative permittivity of the various soil types was estimated using the Topp et al. model. The results obtained put the values of the relative dielectric permittivity of the various soil types between 3.03 for a very dry ground and 10.00 for very wet ground which is an improvement on the values obtained from the Laboratory measurements available in literatures that put the values between 4.5 and 11. The discrepancy in the laboratory results would have come from sample preparations since the soil substructure has been disturbed. The results obtained revealed that the volumetric moisture content is the dominant factor that affects soil electrical property and to a lesser degree the temperature. The diurnal variations of volumetric moisture content were estimated to ascertain the retention of waterin the soil. The results obtained showed that water is evaporated from the soil in relation totheprevailing climatic and weather conditions of the sites of measurement. The fade margins which ascertain the level of signal fades with increase In distance were computedat the frequencies investigated (Amplitude Modulation to Super - High - Frequency bands)using the average values of the relative permittivity and volumetric moisture content obtainedat each location of measurement. The results are useful for circuit design with a view to ensuringlink availability, reliable communication and quality of service for the end users.